CBS News correspondent Randall Pinkston reports that migrants are using this route because U.S. Border Patrol crackdowns such as "Operation Gatekeeper" in San Diego, "Safeguard" in Nogales, Texas, "Hold The Line" in El Paso, Texas, and "Rio Grande" in McAllen, Texas, have closed off most of the traditional border routes.
From February through May, Altar funnels as many as 700,000 migrants north to the border.
Rev. Robin Hoover is the founder of Humane Borders, an organization that sets up water stations in the Arizona desert and warns migrants about its harsh conditions. He says as many as 2,000 migrants will come through Altar in one day.
The migrants know the trek is dangerous, but they feel they have no choice. When asked why he was willing to cross the border at the most dangerous place in the desert, one replied, "Because over here in Mexico I don't got no future."
"We know people die," another said through a translator. "But hunger forces us to do what we don't want to."
The business of Altar is immigration — everything from backpacks to food to lodging.
"The migrants will sleep here just like cigars in a box," Hoover says of a flophouse. "There may be four or more into this little room."
Many residents have turned their homes into rooming houses, charging $5 for a bunk and a shower — and more for migrants who want to wash their clothes and make phone calls.
In the main square, some hire "coyotes" — guides to help them cross the border. Others travel alone. Many pray for a safe journey.
By midday, vans with as many as 40 migrants roll out of Altar, heading toward the border.
The Mexican government's Migrant Protection Agency has set up a checkpoint 42 miles north of Altar. The agent surveys the occupants of the van but doesn't try to turn them around. He does warn them about the danger they will face once they reach the Arizona desert.
The final stop in Mexico is the village of Sesabe. The United States is just on the other side of the hills. Sesabe is the migrants' last chance to buy clothes, food and water. One family is about to cross for the first time and is ready to walk for days. "We trust that God will take care of us," one man says.
As the migrants head for the hills, their journey in Mexico comes to an end. Some won't survive the desert, while others will be caught and returned. But for many, the trip is the beginning of a new life in America.